Three major events happen in organ-specific autoimmunity during disease progression: autoreactive T cells are generated (I), they traffic to the target organ (II), and they destroy the organ (III). Type 1 diabetes (T1D) is a clear example of such a disease. Its incidence is on the rise in developed countries, and the most efficient therapy for T1D is still the provision of insulin. We have been focusing on the studies of T cell homing to the insulin-producing islets, combining in vivo and in vitro approaches for tracing T cells and searching for molecular clues to what drives T cells to the islets. The goal of these studies is to find targets for blocking homing of T cells for therapeutic intervention in T1D. We came to realization that progress in the field was hampered by the inability to follow the fate of individual islets during T cell attack. Clearly, should we have had this possibility in hand, we would progress much faster in understanding the rules of T cell infiltration, and also in following the fate of 2 cells after T cell ablation and test 2 cell regeneration protocols. To achieve these goals, we came up with a simple solution: an abdominal window allowing intravital microscopy (AWIM). We perfected the technique to the point where we can comfortably address many issues related to T cell homing and islet destruction/regeneration. We also will employ a novel whole organ imaging approach to delineate the global features of inflammation in the pancreas during T1D development. Accordingly, we will pursue the following Specific Aims. Specific Aim 1. Further delineate the role of cross-presentation in homing of T cells. Specific Aim 2. Study the homing of naturally activated T cells to the pancreas. .